The biggest drawback to the Trail Manor is you have to set up the trailer every time you stop if you want to use it.
I will echo another poster in this thread. The huge plus of the TM is ease of pulling and slightly increased gas mileage.
The huge plus of the Coachmen is it's already to use when you stop. Think about that if it's raining when you stop for the night.
Before getting my current Koala, I had a Hi-Lo. It was nice in that when pulling the top dropped down to a height no higher than the cab of my pickup. I would still have it, except I could never come to grips with the idea should one of the lift cables break, I'd be SOL. But it was really nice to pull. It got and extra 1.5 miles to the gallon compared to my current trailer.